This invention relates to an improvement in a solar powered tracking device which is then used to drive a concentrating solar collector for concentrating solar radiation, and more particularly, it relates to such a device wherein the radiation received by sensing devices containing a volatile liquid results in a vapor pressure which powers the movement of the device to respond appropriately when subjected to solar radiation of the sun.
The technology of utilizing solar energy is not new. It has been known for many years that solar radiation may be concentrated with mirrors and with lenses to produce temperatures of 1000.degree. F. and higher. Tracking devices in the past have been powered by electric motors, clockwork mechanisms, hydraulic cylinders, and even locomotive engines. Clockwork mechanisms are precise but they frequently are limited as to the maximum size of the control surface that can be turned. Electric motor systems are probably the most common devices in this field but these systems can be costly and complex. The use of hydraulic or pneumatic pistons and cylinders is much less expensive if a self-contained driving system can be developed that does not rely upon electricity, fuel oil, or other purchased energy sources. Among the prior art patents in this field in U.S. Pat. No. 4,027,651 to Robbins in which a V-shaped receiver is fitted with mirrors and shading devices that direct the solar radiation or, conversely, shield the solar radiation from tubing coils containing a heat sensitive fluid which produces a differential pressure on a piston that in turn causes the apparatus to be adjusted so that it points directly at the sun. In U.S. Pat. No. 4,038,972 to Orrison a parabolic mirror concentrates the solar radiation and tracks the sun by an automatic control based on a light sensing apparatus which signals an electric motor to turn the mirror in whatever direction is needed. In U.S. Pat. No. 4,078,549 to McKeen et al., a mirror facing the sun concentrates the solar radiation and is kept in the appropriate position by a light-sensing mechanism which controls an electric motor that moves the mirror by a chain drive.
The present invention is an improvement on the device described in an article by Morrison et al., entitled "Solar Powered Tracking Device", Building Systems Design, Dec./Jan. 1976. The device described in this article comprises a mirror which is parabolic in cross section and has any suitable and convenient length along which at the focus of the parabola is a metallic tube receiving the concentration of radiation striking the mirror and through which flows any suitable fluid which can receive the solar energy. The device is powered to track the sun by means of two hydraulic/pneumatic cylinders whose pistons are fixed to each other in an opposing relationship. The piston rods are joined to each other through a gear rack which is mated to a pinion gear affixed to the axis of rotation of the mirror such that any movement of the gear rack and pinion gear will cause the control surface to rotate about its axis. The two cylinders are powered with the vapor pressure from a refrigerant liquid which forms the working portion of two radiation sensing bulbs containing the liquid and attached to each side of the movable control surface. Appropriate shading devices are located to shade or not to shade the sensing devices from solar radiation when the control surface is not pointed directly at the sun. Only one of the two sensing devices is more exposed to the sun in any given position of the control surface except when it is pointed directly at the sun, in which event both of the sensing devices are partially shaded from radiation. When the control surface is not pointed directly at the sun the more exposed sensing device is heated by the solar radiation to cause an increase in vapor pressure of the refrigerant liquid which in turn causes a corresponding movement of the pistons in the cylinders, and through the gearing arrangement a corresponding movement of the control surface. While this device has many admirable features it does not track the sun with sufficient precision to be acceptable as a practical means for concentrating solar energy.